In the process of manufacturing color filter substrates, the size of a color filter and the overlapping region between the color filter and a black matrix should be strictly controlled to avoid light leakage or overlaps between adjacent color filters. Currently, in this field, the overlapping region between a color filter and a black matrix is determined mainly through the difference of gray-scale values at the edges of the color filter and the black matrix. Specifically, the edges of the overlapping region can be determined through the following steps.
As shown in FIG. 1, an area to be detected is imaged by a charge-coupled element. The area to be detected comprises color filters 1 each having a different color. For ease of distinguishing, the color filters of different colors in FIG. 1 are filled by different patterns. FIG. 2 shows a magnified version of the measurement area to be detected 9 which are indicated by the dashed box in the area to be detected in FIG. 1. The measurement area to be detected 9 comprises an overlapping region 2, and a color filter 1 and a black matrix 3 on each side of the overlapping region. In FIG. 2, the gray-scale value is indicated by the density of the filled pattern. The larger the gray-scale value is, the sparser the filled pattern is, and vice versa. Then, an original gray-scale value curve is drawn as shown in FIG. 3 based on the variation of the gray-scale value from left to right in the measurement area to be detected 9, and a differential gray-scale value curve is obtained by calculating the difference of the original gray-scale value curve. Since the color filter 1 and the black matrix 3 overlap to different degrees, the overlapping region 2 usually comprises a first overlapping region 21 and a second overlapping region 22 having different gray-scale values. Therefore, as shown in FIG. 3, the original gray-scale value curve basically comprises four phases, and the corresponding differential gray-scale value curve comprises three distinct extremums. An engineer can set an extremum range Td, namely the range between the two double-dot lines as shown in FIG. 3. Thus, a detecting device will be able to obtain the three distinct extremums based on the predetermined extremum range Td.
In the prior arts, it is commonly acknowledged that the overlapping region 2 between the color filter 1 and the black matrix 3 can be determined by the first distinct extremum and the third distinct extremum existing along a direction from left to right. However, the inventor found that, as shown in FIGS. 4 and 5, if the engineer fails to set an appropriate extremum range, and if the light intensity is low when imaging, there might be four distinct extremums. Obviously, in such a case, the edges of the overlapping region 2 determined by the above method will not be what they actually are.
In addition, in the process of manufacturing color filter substrates, if the color filter substrate suffers a shift, which is still within an accuracy range, the edges of the overlapping region 2 will also shift, which will render the overlapping region 2 wider or narrower. As shown in FIGS. 4 to 7, when the overlapping region 2 gets wider or narrower, the number of the extremums will be increased (five as shown in FIG. 5) or decreased (two as shown in FIG. 7), in which case, it will be impossible to determine the edges of the overlapping region 2 through the existing method.